Hi Guys,
We're using Jira version 5.2.8, I think with unlimited license for 500 users. I'm not sure that such thing even exists. 
And we're thinking to move forward to the next version or even higher(7.x.x) but there are few questions that are blocking us from moving forward:
1. License. Do we need to buy a new license for 6.x.x or the old one will work fine? Or we'll need to upgrade the license and pay some amount of money for an upgrade?
2. Upgrading processes. What is the safest way to upgrade it? move to 6.1.0 and then 6.4.0? Will the data be okay?
Thanks,